Overview

Mumps is a contagious viral infection commonly acquired during childhood. In the past, medical doctors and scientists have questioned whether the mumps virus could contribute to the development of autoimmune disease, conditions in which the body mistakenly attacks itself.

Despite these worries, no true causal link was established between the mumps virus or the measles-mumps-rubella (MMR) vaccine and most autoimmune disorders, with the exception of immune thrombocytopenic purpura and orchitis. The current associations are still under investigation.

Today, there is growing public concern that viruses and even vaccines may be causing autoimmune disorders. This article reports on the current scientific studies on the role of mumps in triggering autoimmune disorders and hopes to dispel any fears surrounding this topic. Read on to find out more about mumps, autoimmune disorders, and how the mumps virus and the MMR vaccine are thought to potentially be linked to autoimmune disease.

What are mumps?

Mumps is a virus that infects the parotid glands (a pair of salivary glands), characteristically presenting as a painful swelling on the sides of the face, in front of the ears.

Other symptoms can include:

• Difficulty swallowing
• Dry mouth
• Appetite loss
• Mild abdominal pain
• Joint pain
• High temperature
• Headaches
• Nausea
• Tiredness

If you think you may have mumps, contact your GP for a check-up.

Mumps can cause serious complications:¹

• Aseptic meningitis: inflammation of the brain’s protective layer
• Pancreatitis: inflammation of the pancreas
• Encephalitis: inflammation of the brain
• Deafness
• Orchitis in males: inflammation of the testicles
• Oophoritis in females: inflammation of the ovaries

Although extremely rare (occurring in 0.02% of cases), mumps can lead to death.

How mumps is transmitted

Mumps spreads through infected saliva, which can be inhaled from the air near an infected individual or picked up from infected surfaces and transferred into the nose or mouth.

To prevent its spread:

• Regularly wash your hands with soap and water
• Use tissues when sneezing and dispose of them promptly
• Rest at home for at least 5 days after the onset of symptoms

Outbreaks and the impact of vaccines

Mumps incidence has greatly reduced since the introduction of the MMR vaccine. Despite this, it persists and outbreaks occur periodically in different parts of the world. This is thought to be due to the vaccine’s efficacy decreasing after a number of years, which can be mitigated with booster shots when necessary.

Autoimmunity

Autoimmune diseases are characterised by an abnormal immune response that mistakenly targets your body’s own cells. This response can affect the whole body or be specific to an organ. It is believed that this occurs because the virus closely resembles the body’s own cells; hence, after an infection is cleared, the immune response extends to your own body cells.²

Examples of well-known autoimmune diseases include type 1 diabetes, rheumatoid arthritis, multiple sclerosis, lupus, inflammatory bowel disease, and coeliac disease.

Factors known to affect the development of autoimmunity include genetics, age, environment, and viruses. Viral infections play a major role in triggering autoimmune diseases in people with a genetic predisposition.²

The link between mumps and autoimmune disorders

How mumps may trigger autoimmune diseases

There are two mechanisms believed to be involved in mumps-induced autoimmunity:^2,3

• Molecular mimicry: An antigen (a type of protein) on the cell surface of the mumps virus may be structurally similar to a self-antigen (belonging to your own body cells). Hence, the immune system now recognises the self-antigen as if it were the virus.
• Bystander activation: This occurs when a self-reactive T cell (a type of immune cell) is activated by inflammatory mediators released by nearby cells responding to the infection, without the need for self-antigen recognition.

After the infection is cleared, the immune response developed against the virus could continue to attack your own cells, causing long-term (chronic) inflammation and dysfunction within the body.

Autoimmune diseases linked to mumps

Mumps has been associated with many autoimmune disorders, but the evidence is mostly inconclusive about the causal links and mechanisms. The key autoimmune disorders linked to the mumps virus are as follows:

Immune thrombocytopenic purpura

Immune thrombocytopenic purpura (ITP) is defined as a low number of platelets in the blood (thrombocytopenia) due to the immune system attacking the platelets (autoimmune reaction). It causes bruises and bleeding.

Vaccines are generally safe, but adverse reactions can occur. After receiving the MMR vaccine, some children have experienced a sudden and severe decrease in platelet count (ITP).⁴ Immune thrombocytopenia is one of the most frequently reported adverse effects of the MMR vaccine, but very few individuals actually develop this autoimmune condition following the vaccine.⁵ It occurs in up to 4 children every 100,000 MMR vaccine doses.⁸

Although extremely rare, scientists have confirmed that the MMR vaccine causes ITP, but it is because of the measles and rubella components of the vaccine, not mumps.^6,7,9 Importantly, the incidence and risk of ITP are much lower than that seen in the natural state of rubella, and thus the MMR vaccine remains our safest prevention option.⁹ The good news is that most episodes of ITP following the vaccine resolve within 3 months and rarely persist up to 6 months.⁶

Orchitis

During infection with the mumps virus, orchitis (an inflammation of the testicles) is a complication observed in individuals assigned to males at birth (AMAB) after puberty. Although this autoimmune symptom typically resolves itself after the infection is cleared, in very rare cases, it can cause large enough lasting damage significant enough to reduce sperm count and result in infertility.¹⁰

Type 1 (insulin-dependent) diabetes

Type 1 diabetes is an autoimmune disorder where the body mistakenly attacks the beta cells in the pancreas, which are responsible for making insulin. This means that the pancreas can make little or no insulin, a hormone responsible for regulating blood sugar. High blood sugar is what leads to the symptoms of diabetes.

Older studies questioned whether there is a link between the mumps virus, the MMR vaccine_, and autoimmune type 1 diabetes.^11,12,13

A recent systematic review and meta-analysis from 2016 found only a weak association between childhood type 1 diabetes and the mumps virus, implying mumps most likely do not cause type 1 diabetes.¹⁴ Though researchers continue to investigate this association.¹⁵

There is no evidence of a link between the routine MMR vaccine and childhood type 1 diabetes, as according to a 2016 meta-analysis.¹⁶ The vaccine does not cause type 1 diabetes.¹⁷

Despite many older studies raising concerns about a link between Type 1 diabetes and either mumps or the MMR vaccine, these studies ultimately concluded that there is no evidence to support this connection.

Hashimoto’s thyroiditis

Hashimoto’s disease describes an autoimmune disorder in which the thyroid is underactive due to damage caused by the immune system.

Research has found that some patients with Hashimoto’s thyroiditis also had mumps or remnants of mumps present in the thyroid. However,  it remains unclear whether mumps is responsible for the development of the disease or if the presence of the virus is simply a coincidence.¹⁸

Importance of the measles, mumps and rubella vaccination

There is no evidence to support an association between the MMR vaccine and several autoimmune disorders, such as inflammatory bowel disease, type 1 diabetes, and multiple sclerosis, with the exception of short-term immune thrombocytopenia purpura.^5,6,7 Vaccinations remain our best defence against the mumps virus and complications such as autoimmunity.^6,19

The mumps-measles-rubella (MMR) vaccine protects against mumps infection and helps reduce the risk of autoimmune disorders. It is recommended to follow the routine childhood immunisation schedule or to contact your GP if you have not received this as a child.

Conclusion

While certain autoimmune conditions are associated with mumps, it is important to note that none have yet been confirmed to be caused by the virus, with the exception of the well-studied short-term immune thrombocytopenia and the temporary orchitis with potentially lasting damage to fertility in individuals AMAB.

For the overwhelming majority of the population, the MMR vaccine is safe and evidence shows that it does not cause autoimmunity. In rare cases, it may induce a short-term immune thrombocytopenia, that resolves within 3-6 months after administering the dose. However, this effect is believed to be due to the measles and rubella components of the vaccine, not the mumps component.

Further research is necessary to determine the specific role mumps play in triggering autoimmune responses and to help us prevent autoimmune disease. Vaccines remain our best defence and it is recommended to receive the measles, mumps and rubella (MMR) vaccine to prevent potential complications, including autoimmune disorders.